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Idle air adjustment is done using the big brass screws in your fuel throttle bodies. Turning them clockwise should decrease RPM. It is good practice to remove them and clean those orifices with throttle body cleaner at least once a year. They get gummed up with black soot. There are small o rings on them as well that harden up and need replacing now and again.

Adjustment needs to be done with a throttle balancing device unless you have exceptional hearing and experience doing this manually. The baseline setting is accomplished by turning them in all the way gently till they bottom out and back out 1.5 turns on each side. Then you need the balancer (Twin Max, Carb Tune, Harmonizer, mercury stix etc. etc.) attached to the vacuum ports on the bottom (look for small rubber caps) to do this properly.

If this does not do it, dive into this thread and / or many others here :

"There are small o rings on them as well that harden up and need replacing now and again"

I went to, 'Max Stratton's BMW' web-site and looked up the throttle body.
However I did not find the 'o'ring's' you spoke of?

The adjusting screw is part number 18 of the throttle housing assy under fuel preperation fiche on MAX BMW. You are right though, I don't see the O ring listed there either but if you call them I am sure it is available. You can see it in the blowup of the part.

I've never heard of the O-rings being available separately; yeah, a waste...
They are a very tight fit on the BBSs.
If anybody knows the "new unused undistorted" inside and outside diameters, and what material they need to be, that would be a help...

Now that you guys mention this and the fog is lifting in my memory banks I recall this coming up before and yeah, the o rings come with the BBS. Which is just... silly but I guess it costs $6.38 to find out what size that o ring is and then just go dig around my viton o ring kit from harbour freight or wherever ...

Also just remembered a warning to never _ever_ use silicone grease on them either or you can ruin your O2 sensor! A small dab of red rubber grease would be acceptable though.

Now that you guys mention this and the fog is lifting in my memory banks I recall this coming up before and yeah, the o rings come with the BBS. Which is just... silly but I guess it costs $6.38 to find out what size that o ring is and then just go dig around my viton o ring kit from harbour freight or wherever ...

Also just remembered a warning to never _ever_ use silicone grease on them either or you can ruin your O2 sensor! A small dab of red rubber grease would be acceptable though.

Got it! NO Silly grease. Viton O-rings at Harbor Freight. Now what did I do with my 20% discount coupon??